The present invention relates to a part time four wheel drive motor vehicle.
Japanese patent provisional publication No. 58-56922 shows a conventional four wheel drive vehicle which automatically changes the drive system from a two wheel drive mode to a four wheel drive mode when the vehicle traverses a slippery road such as a snowy road. This vehicle has a means for detecting a difference of rotational speed between the front wheels and the rear wheels, and changes the drive system to the four wheel drive mode in accordance with the detected rotational speed difference.
However, this four wheel drive vehicle is unsatisfactory in that the drive system is changed to the four wheel drive mode only after the driving wheels start slipping. In this vehicle, a change to the four wheel drive mode is effected so late that the vehicle stability especially in cornering is injured, and the vehicle is apt to spin out.